Clustering Patterns of Unhealthy Lifestyle Behaviours Among Adolescents: A Multilevel Analysis of a Nationally Representative School-Based Survey from 73 Countries.

: Adolescence is a crucial stage when young people adopt various lifestyle behaviours that can impact their health. However, the broader determinants of these behaviours remain underexplored. This study aimed to investigate clustering patterns of lifestyle behaviours, including physical activity, sedentary behaviour, and dietary habits, among adolescents and examine their determinants across individual, community, and societal levels. : This study utilised nationally representative Global School-based Student Health Survey data. The lifestyle behaviours were dichotomised based on specific definitions, and the clustering patterns of multiple unhealthy behaviours were compared at various levels of factors. Multilevel logistic regression analysis was employed to identify individual, community, and societal level determinants of multiple unhealthy behaviours. : The study included 293,770 adolescents from 73 countries and territories across five World Health Organization (WHO) regions. The overall prevalence of one, two, three, four, and five unhealthy behaviours was 6.9%, 29.9%, 36.5%, 21.5%, and 4.5%, respectively. The odds of multiple unhealthy behaviours (defined by ≥4) increase with age and are higher among female adolescents [(AOR: 1.06, 95% CI:1.05, 1.07); (AOR: 1.16, 95% CI: 1.14, 1.19)], respectively. Adolescents from supportive families, peer environments, or food-secure households had lower odds of engaging in these behaviours [(AOR: 0.84, 95% CI: 0.82, 0.86); (AOR: 0.96, 95% CI: 0.94, 0.98); (AOR: 0.91, 95% CI: 0.87, 0.95)], respectively. The odds of exhibiting multiple unhealthy behaviours were significantly higher among adolescents in countries with high (0.7-0.79) and very high (0.8-1.0) Human Development Indexes (HDI) compared to those in low (<0.55) HDI countries [(AOR: 1.84, 95% CI: 1.16, 2.94); (AOR: 3.00, 95% CI: 1.48, 6.08)], respectively. : The study findings reveal that multiple unhealthy lifestyle behaviours, including insufficient physical activity, sedentary behaviour, inadequate fruit and vegetable consumption, frequent soft drink intake, and fast-food consumption, are globally prevalent among adolescents. These behaviours have distinct clustering patterns associated with individual characteristics, family and peer environments, and broader socio-economic and societal contexts.